1. Related Applications
This application is related to the subject matter of the following applications filed simultaneously herewith, designated with Ser. Nos. 12/612,831 and 12/612,842 and 12/612,856 and 12/613,004 and 12/613,082.
2. Field of the Invention
The present invention relates to an upconversion stage for a local coil array, in particular a local coil array of the type providing phase scrambling for improved resolution in wireless coils magnetic resonance imaging (MRI).
3. Description of the Prior Art
MRI scanners use a combination of a strong constant magnetic field (B0) from a superconducting magnet which is modified by gradient fields generated by gradient coils, together with a rotating magnetic field (B1) from a radio frequency (RF) antenna to excite nuclear magnetic resonances in the body that generate short term RF signals that are received to build up a tomographic image.
All current-generation MRI scanners employ arrays of local coils mounted in close proximity to the scanned patient to receive the RF with maximum possible signal to noise ratio (SNR). The coils that receive signals from the back of the patient are mounted in the patient table. Coils that receive signals from the front of the patient are arranged into ‘blankets’ that are carefully placed over the patient. Associated with each blanket is typically a flexible cable containing one co-axial line for each local coil. The cables potentially interact with the B1 field and with the signals generated from the patient, so ‘traps’ (high impedance sections) must be included at regular (typically λ/8) intervals. These add cost and inconvenience to the structure.
In use, the requirement to connect the cables and sterilize them between scanning one patient and the next leads to increased down-time between scans. It is therefore desirable that the cables be eliminated. However, a wireless solution permitting the cables to be eliminated still needs to substantially satisfy all the requirements of the existing system, particularly with regard to noise.